The present invention is directed to a system for determining the configuration of long towed underwater cables and for calibrating and determining the characteristics of measuring devices which may be displayed along the cable. The present invention is particularly adapted for determining the vertical and horizontal displacement which characterizes long towed arrays and for determining the response characteristics of hydrophones and depth sensors along the array.
A particularly useful system which has been employed for identifying the presence and location of underwater objects has been the long towed array, which essentially consists of a long oil filled tube having dispersed at regular intervals along its length a series of hydrophone elements which detect the presence and location of underwater objects by receiving acoustic sound waves and communicating a signal back to the vessel which is towing the array. Such arrays, however, which may extend for well over a thousand feet in length, characteristically do not assume a linear configuration when towed by a vessel, but rather extend in such a way that the depth and horizontal displacement along the towed array vary considerably.
Accordingly, in order to assure an accurate interpretation of any signal received from hydrophones along the array indicating the presence of an underwater object, it is necessary to calibrate such towed arrays so that the acoustic signal level is known and the characteristic underwater configuration of each towed array is known and taken into consideration in determining the position and characteristics of the underwater object being detected.
Various techniques have heretofore been employed to calibrate acoustic towed array devices such as the dropping of explosive devices which detonate at predetermined depths and the use of acoustic calibration devices which are lowered in the ocean and which emit a known acoustic signal. These techniques, however, have suffered from the disadvantage of not being particularly accurate and also involving considerable expense.
It is accordingly an object of the present invention to provide a system which permits the inexpensive, expeditious and accurate determination of the characteristic underwater configuration of a towed acoustic array or other elongated towed underwater device.
It is a further object of the present invention to provide a device which will permit determination of the position and functional condition of the respective hydrophone elements in a towed underwater array.
It is still a further object of the invention to provide a system which permits the calibration of depth sensors built into underwater towed arrays and to provide performance tests on each hydrophone element in such underwater towed arrays.